In the manufacture of continuous glass filaments, glass is melted in a glass melter or furnace and flows to one or more bushings. Each bushing has a number of nozzles or tips through which streams of molten glass flow. The glass streams are mechanically pulled from the nozzles by a winding apparatus to form continuous glass filaments.
The temperature of the molten glass within the bushing must be high enough to maintain the glass in a liquid state. However, if the temperature is too high, the molten glass will not cool sufficiently so as to become viscous enough to form filaments after passing through the bushing tips. Thus, the glass must be quickly cooled or quenched after it flows from the bushing tips and forms glass filaments. If the glass cools too slowly, the glass filaments will break and the filament forming process will stop.
There are numerous types of apparatus for cooling the glass filament forming area beneath a filament forming machine. A conventional cooling apparatus uses air, water, or both to transfer heat from the filament forming area beneath a bushing and cool the glass filaments. An example of a glass filament forming apparatus is disclosed in U.S. Pat. No. 6,192,714 to Dowlati et al., the disclosure of which is expressly incorporated herein by reference.
Known cooling apparatus can include a plurality of cooling fins. Filaments drawn from the bushing pass on either side of a cooling fin. Heat from the glass is radiantly and convectively transferred to the fins from the glass filaments. The heat passes conductively through the fins and to a water-cooled manifold. Such cooling fins increase the surface area of the cooling apparatus, thereby increasing the amount of heat that can be transferred from the filament forming area.
Typically, a cooling fluid supply, such as water, enters the manifold, travels through a channel, and exits the opposite end of the manifold as a cooling fluid return. The cooling fluid absorbs heat as it flows through the manifold, thereby cooling the manifold, the cooling fins, and indirectly, the filament forming area. However, the amount of heat that such a cooling apparatus can remove from the filament forming area is limited. Heat must travel through the cooling fins and the manifold before it is absorbed by the cooling fluid flowing through the manifold.
Another conventional cooling apparatus includes a manifold and fins, wherein cooling fluid flows from the manifold into a passage (typically U-shaped) in the cooling fin and back to the manifold. However, the amount of heat that can be absorbed by the cooling fluid in such a cooling apparatus is still limited.
If heat can be more rapidly removed from the filament forming area beneath a bushing, the operating temperatures of the bushing and the molten glass in the bushing can be increased, thereby allowing overall throughput to be increased. Accordingly, there is a need for an improved method and apparatus for cooling a filament forming area beneath a bushing to remove a greater amount of heat.